Carbon blacks are generally produced in a furnace-type reactor by pyrolyzing a hydrocarbon feedstock with hot combustion gases to produce combustion products containing particulate carbon black. A variety of methods for producing carbon blacks are generally known.
In one type of a furnace carbon black reactor, such as shown in U.S. Pat. No. 3,401,020 to Kester et al., or U.S. Pat. No. 2,785,964 to Pollock, hereinafter “Kester” and “Pollock” respectively, a fuel, preferably hydrocarbonaceous, and an oxidant, preferably air, are injected into a first zone and react to form hot combustion gases. A hydrocarbon feedstock in either gaseous, vapor or liquid form is also injected into the first zone whereupon pyrolysis of the hydrocarbon feedstock commences. In this instance, pyrolysis refers to the thermal decomposition of a hydrocarbon. The resulting combustion gas mixture, in which pyrolysis is occurring, then passes into a reaction zone where completion of the carbon black forming reaction occurs.
In another type of a furnace carbon black reactor a liquid or gaseous fuel is reacted with an oxidant, preferably air, in the first zone to form hot combustion gases. These hot combustion gases pass from the first zone, downstream through the reactor, into a reaction zone and beyond. To produce carbon blacks, a hydrocarbonaceous feedstock is injected at one or more points into the path of the hot combustion gas stream. The hydrocarbonaceous feedstock may be liquid, gas or vapor, and may be the same or different than the fuel utilized to form the combustion gas stream. Generally the hydrocarbonaceous feedstock is a hydrocarbon oil or natural gas, however other hydrocarbonaceous feedstocks such as acetylene are known in the art. The first (or combustion) zone and the reaction zone may be divided by a choke or zone of restricted diameter which is smaller in cross section than the combustion zone or the reaction zone. The feedstock may be injected into the path of the hot combustion gases upstream of, downstream of, and/or in the restricted diameter zone. Furnace carbon black reactors of this type are generally described in U.S. Pat. Reissue No. 28,974 and U.S. Pat. No. 3,922,335 the disclosure of each being incorporated herein by reference.
In generally known reactors and processes, the hot combustion gases are at a temperature sufficient to effect pyrolysis of the hydrocarbonaceous feedstock injected into the combustion gas stream. In one type of reactor, such as disclosed in Kester, feedstock is injected, at one or more points, into the same zone where combustion gases are being formed. In other type reactors or processes the injection of the feedstock occurs, at one or more points, after the combustion gas stream has been formed. In either type of reactor, since the hot combustion gas stream is continuously flowing downstream through the reactor, pyrolysis continuously occurs as the mixture of feedstock and combustion gases passes through the reaction zone. After carbon blacks having the desired properties are formed, the temperature of the effluent is lowered to a temperature such that pyrolysis is stopped, thereby halting the further production of carbon blacks.
After pyrolysis is stopped, the carbon black containing stream generally passes through a heat exchanger to further cool the mixture.
A disadvantage with many heat exchangers utilized in carbon black production processes is that the combustion air heat exchangers operate in a fouled condition. Fouling occurs through a build-up of carbon black and other deposits on the heat exchange surface, in particular the internal heat exchange surface which comes in contact with the carbon black containing stream.
The fouling of heat exchanger surfaces in a carbon black processes is often cyclical in nature. A period of gradual fouling can be followed by a faster defouling, followed by another period of fouling etc. The fouling of heat exchanger surfaces in a carbon black production process can lead to a number of problems including:
less effective heat transfer resulting in lower air exiting temperatures (lower air preheat) and thus lower carbon black yields and production rates;
less effective heat transfer necessitating higher carbon black stream entering temperatures in order to achieve a desired air exiting temperature, thus increasing the stresses imposed on the heat exchanger materials;
less effective heat transfer resulting in variations in air exiting temperatures which result in variations in carbon black morphology.
an increase in heat exchanger pressure drop, which can result in lower production rates and greater stresses in the heat exchanger materials;
possible equipment damage;
and the tendency of the deposits to harden over time while on the heat exchange surface resulting in the possibility that the hardened deposits will re-enter the carbon black stream contaminating the carbon black product.